1. Field of the Invention
This invention relates to the charging of furnaces and particularly shaft furnaces. More specifically, the present invention is directed to a metering device for controlling the flow of charge material being directed unto the hearth of a blast furnace. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use with a blast furnace. The construction of modern high production blast furnaces has imposed new and more stringent demands on the charging apparatus due in part to the increased internal pressures and the increased dimensions of the surface within the furnace over which the charge must be uniformly distributed. In order to obtain optimal furnace operation, it is necessary to be able to measure and excercise control over all of the operating processes both in and on the furnace. Complete economy of operation particularly requires that the furnace charging process parameters be known and controlled. The distribution and metering of the charge over the furnace cross-section is a matter of primary importance because the profile of the charge provides the basis for the control of further operating processes within the furnace. Considering the large throat cross-sections and the very high pressures and temperatures which occur at the throats of the furnaces presently in use, and taking into account the fact that the charge material may vary in composition and grain size, it will be obvious to those skilled in the art that satisfactory control over the charging process requires the metering of the flow of material into the furnace. Similarly, means must be provided which will permit the rate of flow of material to be varied at will during a charging process.
Prior to the introduction of the furnace charging apparatus disclosed and claimed in U.S. Pat. No. 3,693,812 issued Sept. 26, 1972 to R. Mahr et al, optimal uniform distribution of a furnace charge over the entire charging area was not possible. The apparatus of the referenced patent permits the exercise of control of the charging process over the complete hearth cross-section of the furnace by means of a feed chute rotatably arranged in the furance and angularly adjustable relative to the furnace axis.
U.S. applications Ser. Nos. 339,118 and 339,297, filed contemporaneously herewith, disclose apparatti wherein the weight of the charge material supplied to the furnace may be monitored during the charging process. The apparatti of copending Applications Ser. Nos. 339,118 and 339,297 permit control to be exercised over the charge material supplied to the feed and distribution chute of the apparatus of U.S. Pat. No. 3,693,812 as a function of the required charge for the furnace operating conditions.
The maximum benefits which may be realized through use of the metering apparatus of copending Application Ser. No. 339,118 can be achieved if, in addition to an accurate weight determination of the charge burden, the flow of charge material from a supply hopper to the distribution chute can be regulated by an easily controllable metering member. The conveying means employed in the prior art to transfer charge material from a supply hopper to the furnace have at best had a limited influence on the control or checking of the feeding process and serve either solely for transportation of the charge in the horizontal direction or to insure that the material will not be dropped onto the furnace hearth from too high an elevation. Typical of the prior art hopper-furnace conveying means have been discharge troughs, vibrators and screw conveyors. The movable members of the prior art conveying means are subjected to wear by the constant friction of the charged materials on their surfaces and in practice these conveying devices have had an unacceptably limited life. In the interest of increasing life, efforts have been made to clad the portions of the conveying means exposed to wear with an appropriate hard metal or artificial balsalt. These coating techniques have, however, offered only minor improvements in the operational life of the equipment. A further disadvantage of the prior art conveying means is that such apparatus has been unable to abruptly terminate the flow of charged material into the furnace thereby requiring the incorporation of an additional material stopping member. As will be obvious to those skilled in the art, increases in complexity of the charging apparatus, as for example required by separate conveying and flow shut-off means, not only increases equipment complexity and expense but also encounters space limitation and sealing problems; particularly in the case of high pressure furnaces.